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The invention pertains to the fields of fluid handling and electroosmotic flow. More particularly, the invention pertains to variable potential electrokinetic devices useful as pumps and flow controllers.
Electrokinetic pumps are useful for pumping fluids in a highly controllable manner. In addition, electrokinetic pumps provide advantages over mechanical pumps because the electrokinetic pumps may be manufactured with few or no moving parts. U.S. Pat. Nos. 6,013,164 and 6,019,882 describe the manufacture and use of the first electrokinetic pumps capable of generating pressures in excess of a few pounds per square inch (xe2x80x9cpsixe2x80x9d).
Electrokinetic flow controllers are useful for managing the flow of fluids through conduits and also have the advantage that they may be manufactured with few or no moving parts. U.S. patent application Ser. No. 09/942,884 assigned to Eksigent Technologies LLC describes the manufacture and use of the first electrokinetic flow controllers.
Notwithstanding these advantages, prior art electrokinetic pumps and flow controllers suffer from one or more shortcomings with respect to fluid composition, operating voltages, voltages at connection points to other devices, and pumping efficiencies that limit their use in many fluid handling applications.
U.S. Pat. No. 3,427,978 by Hanneman et al. discloses an electro-hydraulic transducer designed to work with a purified, non-aqueous liquid having a hydrocarbon portion and a polar group and having a dielectric constant between 5 and 100. Furthermore, the devices taught by Hanneman et al. include in the pumping fluid a small amount of redox material so that the oxidation occurring at the anode balances the reduction occurring at the cathode thereby enabling the composition of the ionizing liquid to remain in an operationally stable condition over a period of a number of hours during the continuous application of an electrical potential difference of 200 volts and higher across the electrodes.
U.S. Pat. No. 6,171,067 to Parce provides a micropump that utilizes electroosmotic pumping of fluid in one conduit or region to generate a pressure based flow of material in a connected conduit, where the connected conduit has substantially no electroosmotic flow generated. The devices taught by Parce typically are fabricated using open microscale conduits, and include conduit wall surfaces that have associated charged functional groups to produce sufficient electroosmotic flow to generate requisite pressures in those conduits in which no electroosmotic flow is taking place. Parce also teaches that electroosmotic flow preferably is avoided in the first conduit portion either by providing the first conduit portion with substantially no net surface charge to propagate electroosmotic flow, or alternatively and preferably, electroosmotic flow is avoided in the first conduit portion by applying substantially no voltage gradient across the length of this conduit portion.
Takamura et al. (xe2x80x9cLow-Voltage Electroosmosis Pump and Its Application to On-Chip Linear Stepping Pneumatic Pressure Source,xe2x80x9d in J. M. Ramsey and A. van den Berg (eds.), Micro Total Analysis Systems 2001, pp. 230-232 (2001) Kluwer Academic Publishers, the Netherlands)(which reference is not admitted by applicants to be prior art to the present invention) teach low-voltage electroosmotic flow pumps consisting of narrow conduits and cascade configuration microfabricated on quartz chips. Takamura et al. do not teach, as their FIG. 4 illustrates, how to design and build pumps capable of generating pressures more than about 80 mm H2O (0.1 psi) or 4 mm H2O/volt (0.006 psi/volt), nor do they teach how to within broad limits arbitrarily set the potential at the inlet and outlet connection points of their electroosmotic pump.
The present invention addresses these and other shortcomings of the prior art by providing variable potential electroosmotic devices such as pumps capable of operation over a wide range of fluid composition and operating voltages, that can be fabricated as micro- or macro-scale devices, that are capable of generating considerably greater pressures/volt as compared to the prior art devices, and that can be configured for improved device safety and compatibility by allowing for the control of applied voltage at either or both of the ends of the devices. The present invention also provides improved geometries to enhance performance, safety and compatibility of electroosmotic flow controllers such as those described in co-owned U.S. patent application Ser. No. 09/942,884.
The present invention provides variable potential electrokinetic devices including pumps and flow controllers that have improved performance, safety, operating efficiency, and compatibility with other instrumentation. The present invention achieves these objectives by providing in a first aspect, a variable potential electrokinetic device that comprises a pumping conduit having a first end and a second end, and containing a porous dielectric material; a conducting conduit having a first end and a second end, said pumping conduit second end and said conducting conduit first end connecting at a junction; and an odd number of electrodes in electrical communication with the pumping conduit and the conducting conduit.
In a preferred embodiment, the odd number of electrodes comprises a first electrode at potential V1 in electrical communication with the pumping conduit first end; a second electrode at potential V2 in electrical communication with the junction; and a third electrode at potential V3 in electrical communication with the conducting conduit second end, wherein V1 does not equal V2.
In other preferred embodiments, V1 is equal to V3. This allows safety and compatibility to be optimized, by setting potentials V1 and V3 to, e.g., ground potential.
In another aspect, the invention provides for an electrokinetic device that comprises a pumping conduit having a first end and a second end, and containing a porous dielectric material; a conducting conduit having a first end and a second end, said pumping conduit second end and said conducting conduit first end connecting at a junction; and a first electrode at potential V1 in electrical communication with said pumping conduit first end, a second electrode at potential V2 in electrical communication with said junction, and a third electrode at potential V3 in electrical communication with said conducting conduit second end, wherein a predetermined electroosmotic flow may be generated by said device with at least one of said potentials V1 and V3 assuming an arbitrary value.
In another aspect, the invention provides a multi-stage electrokinetic device having a first pumping conduit having a first end and a second end, hydrodynamic conductance kp, electrokinetic pressure value pekp, and electrical resistance Rp and containing a first porous dielectric material; a first conducting conduit having a first end and a second end, hydrodynamic conductance kc, electrokinetic pressure value pekc, and electrical resistance Rc, the first pumping conduit second end connecting to the first conducting conduit first end at a first junction; a second pumping conduit having a first end and a second end, and containing a second porous dielectric material, said first conducting conduit second end and said second pumping conduit first end connecting at a second junction; and a first electrode in electrical communication with said first pumping conduit first end; a second electrode in electrical communication with said first junction; a third electrode in electrical communication with said second junction; and a fourth electrode in electrical communication with said second pumping conduit second end, wherein pekc/pekp less than 1 is required, wherein kc greater than kp is preferred to maximize performance and wherein Rc greater than Rp is preferred to increase electrical efficiency and reduce electrochemical evolution of the pumping fluid. These design principles also may be applied to the single-stage variable potential electrokinetic devices to obtain similar advantages.
In a related aspect of the multi-stage electrokinetic device, the invention provides for the first electrode to be at potential V1, the second electrode to be at potential V2, the third electrode to be at potential V3, and the fourth electrode to be at potential V4, so that at least one of the differences (V1xe2x88x92V2) and (V3xe2x88x92V4) is not equal to zero. In another preferred embodiment, V1 is equal to V4. This allows safety and compatibility to be optimized, by setting potentials V1 and V4 to, e.g., ground potential.
In yet another aspect, the invention provides for a multi-stage electrokinetic device that includes a first pumping conduit having a first end and a second end, and containing a first porous dielectric material; a first conducting conduit having a first end and a second end, the first pumping conduit second end and the first conducting conduit first end connected at a first junction; a second pumping conduit having a first end and a second end, and containing a second porous dielectric material, the second pumping conduit first end connected to the first conducting conduit second end at a second junction; a second conducting conduit having a first end and a second end, the second pumping conduit second end connected to the second conducting conduit first end at a third junction; and an odd number of electrodes in electrical communication with the pumping conduits and the conducting conduits.
In a preferred embodiment of this multi-stage electrokinetic device, the odd number of electrodes comprises a first electrode at potential V1 in electrical communication with the first pumping conduit first end, a second electrode at potential V2 in electrical communication with the first junction, a third electrode at potential V3 in electrical communication with the second junction, a fourth electrode at potential V4 at the third junction, and a fifth electrode at potential V5 at the second conducting conduit second end, wherein at least one of the differences (V1xe2x88x92V2) and (V3xe2x88x92V4) does not equal zero. In another preferred embodiment, V1 is equal to V5. This allows safety and compatibility to be optimized, by setting potentials V1 and V5 to, e.g., ground potential.
In an alternative embodiment of the multi-stage electrokinetic device, the odd number of electrodes comprises a first electrode at potential V1 in electrical communication with said first pumping conduit first end, and an Nth electrode at potential VN in electrical communication with a second end of a terminal conducting conduit. In yet another preferred embodiment, V1 is equal to VN, which allows safety and compatibility to be optimized, by setting potentials V1 and VN to, e.g., ground potential.
In yet another embodiment, the invention provides for an electrokinetic device that comprises a first pumping conduit having a first end and a second end, and containing a first porous dielectric material a first conducting conduit having a first end and a second end, said first pumping conduit second end and said first conducting conduit first end connecting at a first junction; a second pumping conduit having a first end and a second end, and containing a second porous dielectric material, said second pumping conduit first end connecting to said first conducting conduit second end at a second junction; a second conducting conduit having a first end and a second end, said second pumping conduit second end connecting to said second conducting conduit first end at a third junction; and a first electrode at potential V1 in electrical communication with said first pumping conduit first end, a second electrode in electrical communication with said first junction, a third electrode in electrical communication with said second junction, a fourth electrode in electrical communication with said third junction, and a fifth electrode at potential V5 in electrical communication with said second conducting conduit second end, wherein a predetermined electroosmotic flow may be generated by said device with at least one of said potentials V1 and V5 assuming an arbitrary value.
The invention also provides for methods of using the devices to control the flow of a fluid. In one aspect, the invention thus provides a method of controlling the flow of a fluid by contacting a pumping conduit first end with a fluid; and supplying potential V1 to a first electrode in electrical communication with the pumping conduit first end, potential V2 to a second electrode in electrical communication with the junction and potential V3 to a third electrode in electrical communication with the conducting conduit second end.
In another aspect, the invention provides a method of controlling the flow of a fluid by supplying a pressure-driven flow to said pumping conduit, and modulating said pressure-driven flow by an electroosmotically-driven flow component generated within said pumping conduit.
Other aspects include a method of controlling the flow of a fluid by contacting at least one end of said first pumping conduit or said second pumping conduit of an electrokinetic device of the invention with a fluid; and supplying potential V1 to a first electrode in electrical communication with said first pumping conduit first end, potential V2 to a second electrode in electrical communication with said first junction, potential V3 to a third electrode in electrical communication with said second junction, potential V4 to a fourth electrode in electrical communication with said third junction, and potential V5 to said second conducting conduit second end.
Yet another aspect of the invention provides a method of controlling the flow of a fluid by supplying a pressure-driven flow to a multi-stage electrokinetic device, and modulating said pressure-driven flow by an electroosmotically-driven flow component generated within said first or said second pumping conduit.
The principles and operation of the invention will now be described by reference to the following figures, which are intended to serve as illustrative embodiments but not to limit the scope of the invention.